The proposed research aims to define the functional properties of visual pigments at a molecular level. Specifically, the work focuses on: (1) the mechanisms by which each pigment tunes the absorption spectrum of the chromophobe (ll-cis retinal) to the correct wavelengths, (2) the conformational changes that occur in the visual pigments upon photoexcitation, and (3) the sites of contact between visual pigments and the peripheral membrane proteins with which they interact, transducin/G-protein, rhodopsin kinase, and arrestin/48-K protein. Two complementary approaches will be used. In the first, human and bovine visual pigments will be produced in large quantities in tissue culture cells by expression of their cloned DNAs. Specific mutations will be constructed in these DNAs so as to produce visual pigments with defined alterations. These mutant pigments will be characterized with respect to their spectroscopic and enzymatic properties. ln the second approach, naturally occurring visual pigment variants will be studied in individuals with inherited variations in color vision. These variants are quite common (8% of caucasian males have an inherited anomaly in their color vision) and represent a rich source of material for study. By testing the color vision of human subjects, analyzing their visual pigment genes, and producing the altered pigment we can correlate psychophysical, molecular genetic, spectroscopic and enzymatic data. A rare and clinically significant color vision defect, blue cone monochromasy, will be investigated by molecular genetic methods. These studies should reveal its molecular basis and provide diagnostic DNA probes for genetic counseling. The visual pigments resemble in structure and function many other cellular receptors, including alpha and beta adrenergic, Ml and M2 muscarinic, and substance K receptors. The molecular mechanisms of visual pigment action defined by the proposed studies will therefore be of general interest to pharmacologists and physiologists.